1. Field of the Invention
This invention relates to memory storage media for use with computers, and more specifically to ultra high density memories for use with general purpose digital computers.
2. Description of the Related Art
The widespread use of computers to perform analysis of data and maintain data bases has caused an ever increasing need for rapid storage and access of large quantities of such data. A wide variety of data storage memory devices have been developed. Among the first of such memories were relatively simple arrays of discrete magnetic elements, such as magnetic core memories. Later, a variety of active and semiactive devices, such as semiconductor memories consisting of arrays of flip-flop circuits or electrical charge coupled devices (CCDs), were developed and continue to be used in a wide variety of computers today.
An accelerating need for massive memory for a number of computer applications has led to the development of optical storage media and other advanced memory concepts that provide very high storage densities per square centimeter of active area in Write Once Read Many (WORM) memories. All of these schemes have had benefits and disadvantages that made them effective for certain applications and less effective for other applications. However, to date, no single data storage and readout memory device has demonstrated all of the important characteristics of an ideal storage medium, since they all include operational limitations in some combination of storage size, density, accuracy or access speed.
One important characteristic of such data storage systems is the access time required to retrieve or store a block of information in a storage system comprised of a large amount of digital information. A requirement to randomly access such data, an important feature for many computer applications, places further constraints upon the types of systems and mechanisms of storage and retrieval of the data in such memories. Long access times substantially diminish the benefits that might otherwise be available from a storage medium that provides large storage capacities.
From the above, it may be seen that high density data storage is only meaningful and useful in a computer system if it is combined with reasonable random access times, accuracy in locating and reading out the data and construction requirements that are likely to result in a relatively robust and easily fabricated memory system.
One approach proposed to achieve high density data storage systems has been based upon the concept of the scanning tunneling microscope as originally conceived by Gerard Binning. One such proposal by Calvin Quate, as reflected in U.S. Pat. No. 4,575,822, describes the use of the tunneling current effect in combination with a dielectric layered storage medium. However, such proposals, which rely upon the tunneling currents present when a stylus is placed within approximately 10 angstroms of a surface and voltage is applied to the stylus and media over which it is moved, result in data storage systems that are not practical for a system requiring access times useful in any realistic computer memory system.
Such systems also present severe control and indexing problems, since the clearance between the stylus and the storage medium must be maintained to extremely close tolerances, on the order of a few angstroms (.ANG.), if tunneling currents with reasonable dynamic ranges are to be maintained. These requirements place severe operational constraints on the quality of construction of the device, the dynamic range and accuracy of the stylus drive system and the quality of the ambient environment maintained in the memory if acceptable performance is to be obtained. Even under the most favorable of operational environments, the proposal to use tunnelling current techniques for high density data storage contains many difficulties related to fabrication, thermal control, environmental control and access times.
Therefore, there still exists a need for extremely high density data storage systems that will provide rapid, random access for storage and retrieval of data and may be constructed without the use of exotic materials or manufacturing techniques. Furthermore, it would be extremely beneficial if such a device, unlike proposed storage devices utilizing tunneling currents, could be constructed so that they could be operated in air rather than in the vacuum or another highly controlled environment required for devices using tunneling currents.